Limits...
Oceanic dispersal barriers, adaptation and larval retention: an interdisciplinary assessment of potential factors maintaining a phylogeographic break between sister lineages of an African prawn.

Teske PR, Papadopoulos I, Newman BK, Dworschak PC, McQuaid CD, Barker NP - BMC Evol. Biol. (2008)

Bottom Line: No evidence was found for isolation by distance, and gene flow was bidirectional and of similar magnitude among adjacent populations.In both lineages, the optimum temperature for larval development was at about 23 degrees C, but a clear difference was found at lower temperatures.While larvae of the temperate lineage could complete development at temperatures as low as 12 degrees C, those of the subtropical lineage did not complete development below 17 degrees C.

View Article: PubMed Central - HTML - PubMed

Affiliation: Molecular Ecology and Systematics Group, Botany Department, Rhodes University, 6140 Grahamstown, South Africa. Peter.Teske@bio.mq.edu.au

ABSTRACT

Background: Genetic breaks separating regional lineages of marine organisms with potentially high broadcasting abilities are generally attributed either to dispersal barriers such as currents or upwelling, or to behavioural strategies promoting self-recruitment. We investigated whether such patterns could potentially also be explained by adaptations to different environmental conditions by studying two morphologically distinguishable genetic lineages of the estuarine mudprawn Upogebia africana across a biogeographic disjunction in south-eastern Africa. The study area encompasses a transition between temperate and subtropical biotas, where the warm, southward-flowing Agulhas Current is deflected away from the coast, and its inshore edge is characterised by intermittent upwelling. To determine how this phylogeographic break is maintained, we estimated gene flow among populations in the region, tested for isolation by distance as an indication of larval retention, and reared larvae of the temperate and subtropical lineages at a range of different temperatures.

Results: Of four populations sampled, the two northernmost exclusively included the subtropical lineage, a central population had a mixture of both lineages, and the southernmost estuary had only haplotypes of the temperate lineage. No evidence was found for isolation by distance, and gene flow was bidirectional and of similar magnitude among adjacent populations. In both lineages, the optimum temperature for larval development was at about 23 degrees C, but a clear difference was found at lower temperatures. While larvae of the temperate lineage could complete development at temperatures as low as 12 degrees C, those of the subtropical lineage did not complete development below 17 degrees C.

Conclusion: The results indicate that both southward dispersal of the subtropical lineage inshore of the Agulhas Current, and its establishment in the temperate province, may be limited primarily by low water temperatures. There is no evidence that the larvae of the temperate lineage would survive less well in the subtropical province than in their native habitat, and their exclusion from this region may be due to a combination of upwelling, short larval duration with limited dispersal potential near the coast, plus transport away from the coast of larvae that become entrained in the Agulhas Current. This study shows how methods from different fields of research (genetics, physiology, oceanography and morphology) can be combined to study phylogeographic patterns.

Show MeSH

Related in: MedlinePlus

Larval development of Upogebia africana lineages. Effect of temperature (T) on duration (D, mean ± SD) of successive larval stages and for cumulative larval development of subtropical (white) and warm-temperate (black) U. africana lineages. Regressions fitted to temperatures less than or equal to threshold temperature (see text for further details) are given with fitted parameters, coefficients of determination (r2) and significance level (p). Asterisks denote a significant difference in duration between lineages (based on a Student t-test).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2628387&req=5

Figure 5: Larval development of Upogebia africana lineages. Effect of temperature (T) on duration (D, mean ± SD) of successive larval stages and for cumulative larval development of subtropical (white) and warm-temperate (black) U. africana lineages. Regressions fitted to temperatures less than or equal to threshold temperature (see text for further details) are given with fitted parameters, coefficients of determination (r2) and significance level (p). Asterisks denote a significant difference in duration between lineages (based on a Student t-test).

Mentions: For both lineages the mean duration of development for each zoeal stage and, consequently, also the mean cumulative duration of development decreased sharply with increasing temperature until a threshold temperature was reached, after which duration remained constant or more or less constant (Fig. 5). The threshold temperature for the Zoea 1 was 20°C and for the Zoea 2 and 3 it was 23°C. Each incremental decrease in temperature below these threshold temperatures resulted in a highly significant increase in duration of development. The temperature dependence of duration of development for the Zoea 1 of both lineages at temperatures below the threshold could be described by statistically highly significant linear regressions and for the Zoea 2 and 3 and cumulative duration by power-model regressions (Fig. 5). Slopes of regressions for each zoeal stage and for cumulative duration were significantly steeper for the subtropical lineage (in all cases p < 0.001).


Oceanic dispersal barriers, adaptation and larval retention: an interdisciplinary assessment of potential factors maintaining a phylogeographic break between sister lineages of an African prawn.

Teske PR, Papadopoulos I, Newman BK, Dworschak PC, McQuaid CD, Barker NP - BMC Evol. Biol. (2008)

Larval development of Upogebia africana lineages. Effect of temperature (T) on duration (D, mean ± SD) of successive larval stages and for cumulative larval development of subtropical (white) and warm-temperate (black) U. africana lineages. Regressions fitted to temperatures less than or equal to threshold temperature (see text for further details) are given with fitted parameters, coefficients of determination (r2) and significance level (p). Asterisks denote a significant difference in duration between lineages (based on a Student t-test).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2628387&req=5

Figure 5: Larval development of Upogebia africana lineages. Effect of temperature (T) on duration (D, mean ± SD) of successive larval stages and for cumulative larval development of subtropical (white) and warm-temperate (black) U. africana lineages. Regressions fitted to temperatures less than or equal to threshold temperature (see text for further details) are given with fitted parameters, coefficients of determination (r2) and significance level (p). Asterisks denote a significant difference in duration between lineages (based on a Student t-test).
Mentions: For both lineages the mean duration of development for each zoeal stage and, consequently, also the mean cumulative duration of development decreased sharply with increasing temperature until a threshold temperature was reached, after which duration remained constant or more or less constant (Fig. 5). The threshold temperature for the Zoea 1 was 20°C and for the Zoea 2 and 3 it was 23°C. Each incremental decrease in temperature below these threshold temperatures resulted in a highly significant increase in duration of development. The temperature dependence of duration of development for the Zoea 1 of both lineages at temperatures below the threshold could be described by statistically highly significant linear regressions and for the Zoea 2 and 3 and cumulative duration by power-model regressions (Fig. 5). Slopes of regressions for each zoeal stage and for cumulative duration were significantly steeper for the subtropical lineage (in all cases p < 0.001).

Bottom Line: No evidence was found for isolation by distance, and gene flow was bidirectional and of similar magnitude among adjacent populations.In both lineages, the optimum temperature for larval development was at about 23 degrees C, but a clear difference was found at lower temperatures.While larvae of the temperate lineage could complete development at temperatures as low as 12 degrees C, those of the subtropical lineage did not complete development below 17 degrees C.

View Article: PubMed Central - HTML - PubMed

Affiliation: Molecular Ecology and Systematics Group, Botany Department, Rhodes University, 6140 Grahamstown, South Africa. Peter.Teske@bio.mq.edu.au

ABSTRACT

Background: Genetic breaks separating regional lineages of marine organisms with potentially high broadcasting abilities are generally attributed either to dispersal barriers such as currents or upwelling, or to behavioural strategies promoting self-recruitment. We investigated whether such patterns could potentially also be explained by adaptations to different environmental conditions by studying two morphologically distinguishable genetic lineages of the estuarine mudprawn Upogebia africana across a biogeographic disjunction in south-eastern Africa. The study area encompasses a transition between temperate and subtropical biotas, where the warm, southward-flowing Agulhas Current is deflected away from the coast, and its inshore edge is characterised by intermittent upwelling. To determine how this phylogeographic break is maintained, we estimated gene flow among populations in the region, tested for isolation by distance as an indication of larval retention, and reared larvae of the temperate and subtropical lineages at a range of different temperatures.

Results: Of four populations sampled, the two northernmost exclusively included the subtropical lineage, a central population had a mixture of both lineages, and the southernmost estuary had only haplotypes of the temperate lineage. No evidence was found for isolation by distance, and gene flow was bidirectional and of similar magnitude among adjacent populations. In both lineages, the optimum temperature for larval development was at about 23 degrees C, but a clear difference was found at lower temperatures. While larvae of the temperate lineage could complete development at temperatures as low as 12 degrees C, those of the subtropical lineage did not complete development below 17 degrees C.

Conclusion: The results indicate that both southward dispersal of the subtropical lineage inshore of the Agulhas Current, and its establishment in the temperate province, may be limited primarily by low water temperatures. There is no evidence that the larvae of the temperate lineage would survive less well in the subtropical province than in their native habitat, and their exclusion from this region may be due to a combination of upwelling, short larval duration with limited dispersal potential near the coast, plus transport away from the coast of larvae that become entrained in the Agulhas Current. This study shows how methods from different fields of research (genetics, physiology, oceanography and morphology) can be combined to study phylogeographic patterns.

Show MeSH
Related in: MedlinePlus